/*******************************************************************************
 * Copyright (c) 2012-2017 Codenvy, S.A.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Codenvy, S.A. - initial API and implementation
 *******************************************************************************/
package org.eclipse.che.commons.lang;


import java.io.File;
import java.io.IOException;
import java.util.function.Supplier;

/**
 * Set of util methods for path strings.
 */
public class PathUtil {

    /**
     * Converts path to canonical form via traversing '..' and eliminating '.' and removing duplicate separators.
     * <b>Note:</b> This method works for Unix paths only.
     */
    public static String toCanonicalPath(String path, boolean removeLastSlash) {
        if (path == null || path.isEmpty()) {
            return path;
        }
        if (path.charAt(0) == '.') {
            if (path.length() == 1) {
                return "";
            }

            char c = path.charAt(1);
            if (c == '/') {
                path = path.substring(2);
            }
        }

        int index = -1;
        do {
            index = path.indexOf('/', index + 1);
            char next = index == path.length() - 1 ? 0 : path.charAt(index + 1);
            if (next == '.' || next == '/') {
                break;
            }

        } while (index != -1);

        if (index == -1) {
            if (removeLastSlash) {
                int start = processRoot(path, NullWriter.INSTANCE);
                int slashIndex = path.lastIndexOf('/');
                return slashIndex != -1 && slashIndex > start ? StringUtils.trimEnd(path, '/') : path;
            }
            return path;
        }
        String finalPath = path;
        Supplier<String> canonicalPath = () -> {
            try {
                return new File(finalPath).getCanonicalPath();
            } catch (IOException ignore) {
                return toCanonicalPath(finalPath, removeLastSlash);
            }
        };

        StringBuilder result = new StringBuilder(path.length());
        int start = processRoot(path, result);
        int dots = 0;
        boolean separator = true;

        for (int i = start; i < path.length(); ++i) {
            char c = path.charAt(i);
            if (c == '/') {
                if (!separator) {
                    if (!processDots(result, dots, start)) {
                        return canonicalPath.get();
                    }
                    dots = 0;
                }
                separator = true;
            } else if (c == '.') {
                if (separator || dots > 0) {
                    ++dots;
                } else {
                    result.append('.');
                }
                separator = false;
            } else {
                if (dots > 0) {
                    StringUtils.repeatSymbol(result, '.', dots);
                    dots = 0;
                }
                result.append(c);
                separator = false;
            }
        }

        if (dots > 0) {
            if (!processDots(result, dots, start)) {
                return canonicalPath.get();
            }
        }

        int lastChar = result.length() - 1;
        if (removeLastSlash && lastChar >= 0 && result.charAt(lastChar) == '/' && lastChar > start) {
            result.deleteCharAt(lastChar);
        }
        return result.toString();
    }

    private static boolean processDots(StringBuilder result, int dots, int start) {
        if (dots == 2) {
            int pos = -1;
            if (!StringUtils.endWith(result, "/../") && !StringUtils.equals(result, "../")) {
                pos = StringUtils.lastIndexOf(result, '/', start, result.length() - 1);
                if (pos >= 0) {
                    ++pos;
                } else if (start > 0) {
                    pos = start;
                } else if (result.length() > 0) {
                    pos = 0;
                }
            }
            if (pos >= 0) {
                result.delete(pos, result.length());
            } else {
                result.append("../");
            }
        } else if (dots != 1) {
            StringUtils.repeatSymbol(result, '.', dots);
            result.append('/');
        }
        return true;
    }

    private static int processRoot(String path, Appendable appendable) {
        try {
            if (!path.isEmpty() && path.charAt(0) == '/') {
                appendable.append('/');
                return 1;
            }
            if (path.length() > 2 && path.charAt(1) == ':' && path.charAt(2) == '/') {
                appendable.append(path, 0, 3);
                return 3;
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return 0;
    }

    private static final class NullWriter implements Appendable {

        public static final NullWriter INSTANCE = new NullWriter();

        @Override
        public Appendable append(CharSequence csq) throws IOException {
            return this;
        }

        @Override
        public Appendable append(CharSequence csq, int start, int end) throws IOException {
            return this;
        }

        @Override
        public Appendable append(char c) throws IOException {
            return this;
        }
    }
}
